In the electronics industry, a majority of “wet processes” such as electroplating, use chemical baths having chemical species therein to interact with a workpiece or object placed in the bath, e.g., to change the workpiece surface such as adding a film or plate to the workpiece surface. For example, semiconductor wafers are deposited in reservoir baths or wells containing a metal solution such as Nickel (Ni) or an alloy such as solder.
These Ni (or other) metal solutions in the chemical baths often include wetting agents, e.g., organic compound additives that may affect several properties of the nickel deposit, e.g., prevent pore formation, prevent electrophoretic deposition of impurities on the surfaces, etc.
In the case of Nickel plating baths, the tooling is designed to avoid excessive generation of Ni vapor phase chemistry as per Environmental Protection Agency. Thus, a known concentration of surfactants, e.g., wetting agents (referred to herein as “organics”), is used in the Ni plating chemistry to meet Environmental Protection Agency requirements. Current techniques perform “blind” additions of the minimum wetting agents (i.e., added to plating chemistry such as a surfactant, e.g., Triton™ X-100 (Trademark of the Dow Chemical Company) to meet EPA requirements. If a minimum is 0.1 ml per liter and (surfactant) is required, it is important that the wetting agents do not leave or escape the plating bath or solution.
However, it has been found that the organic chemical species present in plating bath solutions have a tendency to rise, i.e., “walk up” or “climb”, the side of the reservoir well or bath structure, e.g., to a location above the liquid level line. Further, it has been observed that, over time, the organics tend to wash back down into the plating chemistry leading to excess organics in the bath. For a nickel (Ni) plating bath, the concentration of organic compounds such as wetting agents may increase from 0.4 mL/L to 1.5 mL/L when the bath level rose in the reservoir. Given an upper specification limit for wetting agent concentration in the bath at 0.9 mL/L. would lead to a down time on the tool for an extended period, e.g., 1 week, while the organics were slowly removed using dummy plating and dilution.
While a current option exists to use dummy plating that would consume a small amount of the organics and dilute the bath until the concentration was reduced below the upper specification limit, this does not address the fundamental problem of eliminating the climbing of organics up the reservoir wall and leaving the plating chemistry.